1. Field of the Invention
The present invention relates to a bone-conduction speaker and more specifically to a speaker of a type for listening to sounds by abutting to a head to transmit vibrations of a diaphragm to the skeleton structure.
2. Description of the Related Art
One as shown in FIG. 6A has been known as a conventional bone-conduction speaker. It comprises a cylindrical case 21 having a diaphragm 22 at a top surface thereof, a cylindrical magnet 23 fitted within the case 21, a yoke 25 having a center magnetic pole 24 at the center and fitted at the lower part of the case 21 and a voice coil 26 disposed so as to surround the center magnetic pole 24 of the yoke 25.
The conventionally known bone-conduction speaker has had the structure as described above and those components are disposed concentrically in order, from the center, of the center magnetic pole 24, the voice coil 26, the magnet 23 and the case 21 as shown in FIG. 6B. Accordingly, in order to increase the diameter of the center magnetic pole 24 and to increase a number of turns of the voice coil 26 to enhance the output efficiency, the magnet 23 and the case 21 surrounding them must be enlarged and the increase of the size of the outer diameter is inevitable.